title: Resistance and behavioural response of Plutella xylostella (Lepidoptera: Plutellidae) populations to Bacillus thuringiensis formulations.
abstract: BACKGROUND
  Insecticide resistance is probably the major cause of control failure of Plutella xylostella (L.) in Brazil. In most production regions, the use of chemicals has been the prevalent method of control, with reduced efficacy through cropping seasons, even for the most recent use of products based on Bacillus thuringiensis (Bt). The current status of the resistance to these products was assessed, as well as the behavioural response of P. xylostella populations to Bt sprays.
  
  
  RESULTS
  Most populations of P. xylostella were resistant to Bt products, particularly to Xentari®WDG (2-54-fold). Differences in walking characteristics of larvae were variable for most populations, for both Dipel®WP and Xentari®WDG, but not associated with resistance. Most females preferred to lay eggs on untreated surfaces and showed a reduced proportion of oviposition on treated surfaces that only correlated with resistance to Dipel®WP (r = -0.74, P = 0.02).
  
  
  CONCLUSIONS
  Broad and indiscriminate use of Bt-based products has selected Brazilian P. xylostella populations to resistance. Larval movement appears to be a resistance-independent mechanism. Most populations of P. xylostella preferred to lay eggs on Bt-free surfaces, which might be a result of growers' practice of spraying the cabbage head. Reduced oviposition on treated surfaces correlated with physiological resistance, suggesting a behavioural response among the Bt-resistant colonies to Dipel®WP.
authors.affiliation: Departamento de Produção Vegetal, Universidade Federal do Espírito Santo, Alegre, ES, Brazil.
authors.forename: Hugo B
authors.initials: HB
authors.lastname: Zago
authors.forename: Herbert Á A
authors.initials: HÁ
authors.lastname: Siqueira
authors.forename: Eliseu J G
authors.initials: EJ
authors.lastname: Pereira
authors.forename: Marcelo C
authors.initials: MC
authors.lastname: Picanço
authors.forename: Reginaldo
authors.initials: R
authors.lastname: Barros
mesh_terms: D000818:Animals; D001413:Bacillus thuringiensis / Q000502:physiology*; D019607:Brassicaceae / Q000469:parasitology; D001938:Brazil; D005260:Female; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology; D007814:Larva / Q000187:drug effects / Q000254:growth & development / Q000382:microbiology / Q000502:physiology; D008297:Male; D009036:Moths / Q000187:drug effects / Q000254:growth & development / Q000382:microbiology* / Q000502:physiology*; D010058:Oviposition; D010572:Pest Control, Biological; D010935:Plant Diseases / Q000469:parasitology
chemical_list: D007306:Insecticides
keywords: control failure; diamondback moth; fitness cost; microbial insecticides; survival